1. Field of the Invention
The present invention relates to an illumination device. In particular, the present invention relates to an illumination device for controlling the light distribution of light emitted from a light source by using an optical element.
2. Description of the Related Art
Generally, in an illumination device, various light distribution characteristics are required depending on installation environment in which the illumination device is installed. For example, for a street light (road light) of a type that is installed to stand beside a road, light distribution characteristics different from each other are often required in a road traffic direction and a road width direction orthogonal to the road traffic direction. Typically, in the road traffic direction, a so-called batwing light distribution is required for the purpose of uniformly illuminating a wide range. On the other hand, in the road width direction, an asymmetric light distribution for mainly illuminating the road side from the erected position of the street light is required.
The batwing light distribution refers to a bimodal light distribution pattern that has a peak in two angular directions opposite to each other from the lower side in the vertical direction of the illumination device. With this light distribution, a uniform horizontal illuminance distribution (e.g., illuminance distribution on the road surface) can be achieved over a wide range. In addition, a predetermined vertical illuminance distribution (e.g., illuminance distribution required for illuminating a pedestrian on walkways and crosswalks, from the viewpoints of safety, etc.) can be achieved.
Conventionally, in order to achieve such light distribution pattern, an illumination device for controlling the light distribution of light emitted from a light source by using an optical element has been suggested (e.g., see JP-A-2014-093233).
However, in the illumination device disclosed in JP-A-2014-093233, a bulky lens body is used as the optical element for controlling the light distribution of the illumination light. Therefore, it may be difficult to reduce the size and thickness of the optical element, eventually, the illumination device. Further, since an emitting surface of the lens body is configured by a plurality of complex three-dimensional curved surface, there may be a problem that the mass-productivity (productivity) is low. Further, the batwing light distribution described above is a light distribution characteristic that is not limited to the application of the street light but widely required in other illumination applications, such as a ceiling light for indoor illumination. Accordingly, an illumination device for achieving the batwing light distribution, which is small and can be easily mass-produced, is also in strong demand.